A comparison of the skeletal neuromuscular and autonomic ganglion-blocking potencies of five non-depolarizing relaxants.

1 Results from in vitro experiments on the phrenic nerve-diaphragm and the hypogastric nerve-vas deferens preparations of the guinea-pig have been used to plot log concentration-effect curves for skeletal neuromuscular and ganglion blockade, respectively, for (+)-tubocurarine, pancuronium, alcuronium, gallamine and fazadinium (AH 8165). 2 From the log concentration-effect curves, EC50S and equipotent ratios were calculated. The order of neuromuscular blocking potency was pancuronium = alcuronium > (+)-tubocurarine > fazadinium = gallamine. The ratio EC50 for ganglion blockade/EC50 for neuromuscular blockade was 2.3 for fazadinium, 6.7 for (+)-tubocurarine, 22.9 for alcuronium, 24.3 for gallamine and 200.0 for pancuronium. 3 For pancuronium and gallamine there was a range of concentrations below those producing ganglion blockade at which the response of the vas deferens to hypogastric nerve stimulation was augmented. 4 The results are compared with some of those available in the literature, measured on other species by other methods.